Question 37 QMED03 - Oiler

The Correct Answer is D **Explanation for Option D (Deaerating feed tank via the auxiliary exhaust steam line.):** The main feed pump (MFP) drive turbine operates using steam (usually extraction or auxiliary steam). The purpose of this turbine is to convert the steam's thermal energy into mechanical energy to drive the feed pump. After the steam has passed through the turbine, it is relatively low pressure and low temperature (exhaust steam). This steam still contains significant thermal energy, which is highly valuable for boiler feed water (BFW) heating and deaeration. The Deaerating Feed Tank (DFT) requires low-pressure steam to strip dissolved gases (like oxygen and carbon dioxide) from the BFW and to heat the water before it enters the boiler. Therefore, the exhaust steam from the MFP drive turbine is routed directly into the DFT via the auxiliary exhaust steam line, maximizing plant thermal efficiency by reusing this waste heat. **Why the Other Options are Incorrect:** * **A) SSTG condensers via the auxiliary exhaust steam line:** SSTG (Ship Service Turbo Generator) condensers are only used for the exhaust steam from the SSTG turbine itself, primarily on vessels. While the auxiliary exhaust line might connect to the SSTG exhaust system, the primary and most efficient destination for MFP turbine exhaust steam is the DFT, not the main condensing system (which is generally reserved for main propulsion or high-capacity power generation turbine exhaust). * **B) Main condenser via the auxiliary exhaust steam line:** While the main condenser is the ultimate sink for low-pressure steam if it cannot be used elsewhere, routing MFP turbine exhaust directly to the main condenser would be inefficient. The energy in that steam would be dumped into the cooling water rather than being used to heat the vital boiler feed water in the DFT, leading to a significant loss of heat and increased demand for steam extraction elsewhere to heat the DFT. * **C) Deaerating feed tank via the main feed pump discharge line:** The main feed pump discharge line carries high-pressure water ($P_{discharge} > P_{boiler}$), not low-pressure steam. Steam cannot be injected into the high-pressure discharge line to the DFT, as the pressure differential is completely wrong. Steam is injected directly into the body (steam space) of the DFT, which operates at a relatively low pressure.